1. Field of the Invention
This invention relates to the dyeing of cotton and blended fabric materials, in the form of yarn, fabric, or articles of clothing, in a batch or continuous process.
2. Summary of the Background Art
Indigo, being one of the longest-known coloring agents, has been used to dye cellulose-based textiles, such as cotton, for centuries. However, since indigo is practically insoluble in water, ether, alcohol, and dilute acids, conventional dyeing processes include reducing the indigo dye to a soluble leuco form having an amber color, using a suitable reducing agent with an alkaline material. After the fabric material is then exposed to the leuco form in a bath, the fabric material is exposed to air or oxygen so that the reduced dye within the fabric is oxidized, returning to an insoluble form in which the blue color is apparent. Since, even in the leuco form, indigo has a low affinity for cellulosic materials, these steps are repeated as often as needed to obtain the desired shade of blue, with five to seven immersions typically being used, and with each of these immersions being followed by an oxidation process.
Commercially successful processes for dyeing cotton fabrics with indigo have been generally limited to continuous processes for dyeing warp yarn to be used in the production of blue jeans and other denim products. Such a continuous process is described, for example, in U.S. Pat. No. 3,457,022 as a process in which the yarn is first dipped in hot dye solutions to achieve maximum penetration of the dye within the yarn, which is then repeatedly dipped in cold dye solutions to obtain the desired color.
Other patents describe the chemical components of the dye bath. For example, U.S. Pat. No. 4,166,717 describes a process in which the indigo is reduced to its soluble leuco form with sodium hydrosulfate and maintained in an aqueous solution with sodium hydroxide. An aldehyde addition product, such as formaldehyde, acetaldehyde, or furfural, is added to the solution, with an adduct, such as a bisulfate or a sulfoxylate.
U.S. Pat. No. 5,935,273 describes a process for the continuous dyeing of yarn containing cellulose in a single passage through an aqueous solution of indigo in its reduced, or leuco, state in a dye liquor additionally containing deoxidants, alkali, and a dissolved alkali metal salt at a concentration of 100 to 200 grams/liter as an electrolyte as a pH value of the liquor is adjusted to about 10.2 to 11.3. As the electrolyte concentration is maintained, the yarn is exposed to a gas that dissolves in the aqueous solution while forming an acid. Suitable gasses are carbon dioxide, hydrogen chloride, formic acid vapor, and acetic acid, with carbon dioxide being preferred, with the use of carbon dioxide to establish maintain and control pH in dyeing processes being further discussed in U.S. Pat. No. 5,295,998, and with the use of carbon dioxide to effect an accelerated neutralization of cellulose textile substrates being additionally discussed in U.S. Pat. No. 4,536,907. Then the reduced indigo in the yarn is oxidized to form a pigment, with the dyeing process.
The conventional process includes labor-intensive steps associated with the handling of the yarn, such as warp beam make-up and yarn quilling. To eliminate such steps, what is needed is a method for dyeing garments instead of the yarn used in their production. Additionally, dying garments provides for effective inventory control, and for the color coordination of garments containing different types of yarns or knitted and woven materials.
U.S. Pat. No. 4,845,789 describes a process for the rapid dyeing of a series of successive garments or batches of garments with a vat dye, preferably indigo dye. While the garments are being constrained, they are submerged in, and impregnated with, a dyeing solution in a first bath. Then, they are removed from the first bath and held with the draining from them to be conserved for reuse. Next, the garments are promptly immersed in an oxidizing solution in a second bath to shock oxidize the dye present in the garments, which are then removed from the oxidizing bath while draining the oxidizing solution and preserving it for reuse. The garments are then washed and dried. The time between removal of the garments from the dyeing solution and their placement in the oxidizing solution is less than five minutes.
U.S. Pat. No. 4,756,037 describes a process for dyeing with a vat dye, such as an indigo dye solution, a series of successive garments made with fabric containing cellulose. The garments are supported on supports that keep all fabric surface's of each garment accessible to treating solutions, so that the materials are uniformly impregnated with a dye solution at a first bath. The garments are then inserted in an oxidizing solution within a second bath to uniformly oxidize the dye present within each garment.
The patent art additionally describes a number of methods for treating cellulosic material and blends including cellulose to improve dyeability for dye materials other than indigo. For example, a method for producing anionically dyeable smooth dry crosslinked cellulose is described in U.S. Pat. No. 5,298,584, with a cellulose-containing material being modified with a combination of a hydroxyalkylamine or a hydroxyalkyl quaternary ammonium salt, one or more glycols, and a crosslinking agent. The reaction is typically catalyzed with salts such as zinc nitrate or magnesium chloride, used either alone or in conjunction with citric acid. Types of usable anionic dyes include acid, direct, and reactive dyes. The cellulose-containing material may be in the form of fibers, yarns, slivers, and paper. U.S. Pat. No. 5,139,530 describes the production of anionically dyeable smooth-dry crosslinked cellulosic materials by treatment of methylolamide crosslinked cellulosic materials with an alkali swelling agent such as sodium hydroxide before dyeing. U.S. Pat. No. 3,576,589 describes a method for dyeing a fabric, such as a polyester/cotton fiber, in a vat/disperse dye system, using hydroxylamine sulfate under conditions of thermal fixation. The hydroxylamine sulfate is maintained at a pH in the range 5.0 to 6.5 in a vat/disperse dye pad to obtain maximum penetration of the dye within the fibers of the fabric. U.S. Pat. No. 4,767,421 describes a method of manufacturing a homogeneous water-insoluble dye layer on a substrate, with a solution of a cationic or anionic dye in an organic solvent being provided on the substrate, with the solvent being removed, and with the resulting dye layer being treated with am aqueous solution of a salt. The cation of the anionic dye is exchanged for the cation of the salt. Alternately, during treatment with an aqueous solution of a salt or acid, the anion of the cationic dye is exchanged for the salt or acid.
What is needed is a method for dyeing fabrics and garments formed from fibers including cellulose with indigo, as well as for dyeing the yarn used to make such fabrics and garments. Additionally, what is needed is a method for dyeing fibers including cellulose without relying on multiple dips to get a suitable shade. Furthermore, what is needed is a method allowing the use of batch processes, such as pad-jig dyeing and dyeing within a rotary dyeing machine to dye cellulosic materials with indigo.